Asynchronous transfer mode is a standardised data communications protocol and method for transferring information within a telecommunications network, e.g between two telephone exchanges. ATM operates as a cell relay mechanism wherein data is grouped into fixed length packets or cells. The cells comprise a header and a payload. The header identifies the payload and the payload can comprise video, image, bursty data or voice communications. By providing fixed length cells, information can be handled in a more reliable fashion by switches.
ATM is becoming a common technology for local area networks, metropolitan area networks and wide area networks, since all traffic types can be mixed in the same network, bandwidth can be rapidly reassigned on demand and information rates are scalable to very high speeds.
Data transmission speeds are increasing: switches need to cope with the increased data rates.
Switches determine the transmission path followed by a signal e.g. a signal from a telephone is directed via a private branch exchange to a particular communications link towards a destination telephone. The switches will have, typically, a number of inputs and a number of outputs. Obviously other types of switches occur having a single input or output.
In an m.times.n electrical switch, signals arrive at an input and are routed to any one of n output. The input signals however need to be amplified before further processing and thus, associated with each input there is an amplifier to amplify the signal before being routed across the switch by transistor switching means to a desired output. Two arrangements are presently in use. In the first case, when a signal is input through a particular input, the associated amplifier is switched on and a certain delay is apparent before the amplifier becomes fully operational due to reactive effects in the amplifier circuit. As switching speeds increase to nanoseconds this delay can be a serious problem. In the second case, the amplifier remains switched on so as to reduce amplifier initialisation problems; this method, however, incurs reactive coupling effects between adjacent amplifiers and signal quality is diminished. As data rates increase, reactive coupling effects increase.
The present invention seeks to provide a switch whereby the aforementioned problems are minimised.